Electronic systems such as personal computers (PC's) often use small printed-circuit board (PCB) daughter cards known as memory modules instead of directly mounting individual memory chips on a motherboard. The memory modules are built to meet specifications set by industry standards, thus ensuring a wide potential market.
FIG. 1 shows a memory module. Memory module 10 includes one or more dynamic-random-access memory (DRAM) chips 18 that are accessible through one or more rows of metal contacts 12 that fit into a socket on the PC motherboard. Memory module 10 also contains buffer chip 20. Notches 14 and hole 16 may be included to assist with alignment when inserting memory module 10 into a socket. Additional components such as capacitors (not shown) may also be present on the printed-circuit board (PCB) substrate of memory module 10.
FIGS. 2A-B show a memory module being inserted into a memory module socket mounted to the top surface of a PC motherboard. In FIG. 2A, memory module 10 contains DRAM chips 18 and buffer chip 20.
PC motherboard 28 is a larger PCB than memory module 10. PC motherboard 28 has chips, sockets, and other components mounted thereon, such as chip 32 and expansion sockets 36 which have expansion cards 34 plugged in. Expansion cards 34 can be Peripheral Component Interconnect (PCI), PCI Express (PCIe), AT-bus, or other expansion cards. Chip 32 can be the main microprocessor, chip set, cache memory, or other chips.
Memory module socket 26 is one of several sockets designed to fit memory module 10 or other memory modules. Memory module socket 26 is mounted to the top flat surface of the PCB substrate of PC motherboard 28, and fits the contact pads on the bottom side of memory module 10. Typically there are two or four memory module sockets 26 on PC motherboard 28.
FIG. 2B shows the memory module plugged into the PC motherboard. The contact pads on memory module 10 fit into memory module socket 26 on PC motherboard 28. Electrical contact is made by memory module socket 26, with wiring traces and metal contacts 12 on memory module 10 passing most signals through from PC motherboard 28 to DRAM chips 18 on memory module 10.
While the standard PC motherboard with perpendicularly-mounted memory modules are useful, the overall height of PC motherboard 28 is increased by the perpendicular mounting of memory module 10 and memory module socket 26, which is mounted to the top surface of PC motherboard 28. Since expansion cards 34 are also mounted perpendicularly, and are much larger than memory module 10, memory module 10 appears to be insignificant. However, the functions performed by expansion cards 34 are often integrated onto chips 32 that are surface mounted to PC motherboard 28, so the need for expansion cards 34 is diminishing. Some systems may not require expansion cards 34.
Some systems have an ultra-thin height. For example, tablet computing devices (tablets) and ultrabooks require that the height be less than the height of a perpendicularly-mounted memory module. These devices may mount memory chips directly onto a motherboard rather than use plug-in memory modules. Thus the desirable aspects of removable memory modules such as ease of inserting different sizes of memory is lost.
Specialized systems such as servers, parallel processing systems, storage farms, or motherboard-based testers may include many PC motherboards 28 that are tightly packed together into a small volume of space. The pitch or spacing of an array of PC motherboards 28 stacked on top of each other in a rack may be limited by the height of each PC motherboard 28 and its components such as memory module 10. These systems may eliminate expansion cards 34 by integrating their functions onto PC motherboard 28. Thus the height of these systems may now be limited by memory module 10 inserted into memory module socket 26.
What is desired is a reduced-height PC motherboard. A low-profile motherboard is desired that still uses standard memory modules.